For a quiz today, we had to write out a small composition on the subject of summer vacation. Here is what I came up with. Please help with corrections (basic Japanese so don't expect anything glamorous ^_^). Thank you!

Sorry to say, but there are a lot more mistakes than the ones Rich pointed out. Most of them are less grammatical and more "These phrases don't exist in Japanese." But I am going to defer to one of the better Japanese speakers on the board instead of embarassing myself trying to fix them myself.

Your Japanese is pretty good rather than wrong except some parts of the sentences, I think. Most of problems seem to be only depending on whether the sentences sound native or nonnative.

子供の時、夏の休みの意味はおじいちゃんの畑で遊びました。

夏休み:summer vacation夏の休み:holiday in summer (if you want to meaning so, it might be better to use "休日", because "休み" sometimes means a break).

（私の）夏休みの意味は遊ぶことでした。（私は）夏休みに遊びました。

As Harisenbon-san said, the subject of this sentence is "意味". So, if the subject ended with the verb "遊ぶ", it means "meaning played". It might be a little funny.

子供の頃は、私にとって夏休みといえばおじいちゃんの牧場で遊ぶことでした。

毎週の日曜日にいつもおいしい食べ物があったし、かわいい動物がいったし、家族とおじいちゃんの家に行きました。

In this sentence, the object which is modified by "いつも" seems to be ambiguous. So, it could mean both "there had been always tasty food" and "in Sunday always I had gone to my grandpa's home", I think. From the context, it seems to mean later one.

Certainly, "___ったし" repeats are used at conversation in Japanese (especially among the girls in teenager). But, on the basis, it is better that the last one is ended with "__ので", I think.

おいしい食べ物があったし、かわいい動物がいたので、毎週日曜日には、いつも家族とおじいちゃんの家に行きました。

そのごろ、従姉や弟と近く森で走ったり牛の田で遊んだりしてもいいでした。

It was difficult to understand to me what "いいでした" meant. However, it is not serious problem whether it means "good thing" or "to allow", I think.

そのころは、従姉や弟と近くの森で走ったり、牛の放牧地で遊んだりして過ごしました。At the time, I had spent the days running in the forest nearby, and playing on the grazing land of the cow with my cousin and my younger brother.

それから、ハンバーガーやフライドポテトをたいてい食べました。

If the sentence before it was ended with "遊びました/過ごしました", "それから" could use for connection of the sentences. I think, the sentence before it seems to be ended with your thought or feeling. If it is so, to use "遊んだ後は(after playing)" might be suitable.

遊んだ後は、たいていハンバーガーやフライドポテトを食べました。

私はおじいちゃんみたいに強くなりたいと思いましたから、馬屋で働いて牛に食べ物をあげて馬に乗ってみました。

I think "思いました" (a past form of "思う") is suitable to use in the case that the thought is still not changing. In this case, your thought seems to be changing from it. So, it might be suitable to use "思っていました" instead of it.And in this case, "馬屋で働いて牛に食べ物をあげて" and "馬に乗ってみました" seem to be independent behavior, but not to be continuous. From this reason, I think it is better to use "__たり" form to connect the sentences.

厩舎: a stable (馬屋, 馬小屋); a cowshed (牛舎)

私はおじいちゃんみたいに強くなりたいと思っていましたから、厩舎で働いて牛に餌をあげたり、馬に乗ってみたりしました。

でも、大人になった時、私はおばあちゃんみたいに画工になりました。今、絵をかくのほうが畑で働く事より好きです。

These sentences seem to mean that the things you like were changed. In this case, to use "今では/今は" to express the contrast of past days and nowadays might be more suitable. And, to add "事" also to "絵を描く" is needed.

今では、絵を描く事のほうが畑で働く事より好きです。

このごろ、週末、家族はおじいちゃんの畑にもう行きません。

最近では、もう週末に家族でおじいちゃんの畑に行く事はありません。

私の夏は仕事をする事だけです。

My summer meanings become only working.(?) I think it is more better this sentence expresses the meaning of the counterpart of the first line.

夏といえば仕事ばかりになっています。My summer is becoming only working.

でも、おじいちゃんの畑の夏の休みはまだ覚えられます。

"まだ覚えられる" means "to be able to remember relatively" in Japanese.

でも、おじいちゃんの牧場で過ごした夏休みは今でも覚えています。

(Please point out my mistake of English. Any correction will be appreciated.)

Thank you for your replies. Actually, we have to rewrite this and do it again for a quiz today. I will use these suggestions in my new composition. Some of the sentences might have sounded weird in the first part because we had to use certain things (comparative, already/not yet/still, want/want to, have to/must not/may, etc.) so I tried to fit those things in where I thought they would go.

Luckily, even with the sentences you provided, I have all that I need. I have to study and memorize this new version so that I make sure to understand some of the new grammar. ^_^ I'm not a big fan of memorizing without understanding.

に after an expression of time, で after a description of the group doing the activity （一人で、二人で、みんなで、などなど）; は in its contrastive capacity (you may do other things on the weekend, you may do other things as a family, but you no longer go as a family on the weekend to Grampa's farm.)

Hmm... my teacher insisted on teaching us 遣る【やる】 for giving to inferiors, especially for animals. She even told us that it might be used to say "I gave to my child...", but it might be more antiquated than she thinks. After all she DID move to Greece from Japan 40 years ago.